Several companies offer direct-to-consumer genetic testing. These tests generally are single nucleotide polymorphism (SNP) tests, in which variations within the DNA that have been associated with different diseases or traits are tested. The association between SNPs and disease risk is investigated by genome-wide association studies, or GWAS.
Using GWAS to find genetic links to disease is different than evaluating a known disease gene for a mutation that affects the gene function. Some SNP tests are tailored to look for a specific risk, such as colon cancer or heart disease. Other tests evaluate dozens of diseases and traits and report them all. The list of conditions that are reported might range from things like cancer and diabetes to HIV susceptibility and earwax production. Typically the test kits are sent to the consumer by mail, and the results are mailed directly to the consumer.
You will likely encounter a patient who will bring you his or her SNP risk test results and ask you to make a health care recommendation. It’s important to know that the accuracy in predicting disease risk from SNP testing generally is not well validated, and these tests have largely not been endorsed by the medical community. While it might be fun for patients to find out if they have a genetic change that causes them to make more earwax, the utility of these tests is somewhat limited.
Often, family history and lifestyle factors are better predictors of diseases such as cancer, diabetes, and heart disease. Because they may explain only a small portion of the heritability of disease, SNP risks need, at a minimum, to be interpreted in light of family history and lifestyle factors.
It’s important for individuals who are considering SNP testing to understand the limitations of these tests, as well as the significance of other factors affecting their risk and how SNP panels might include information about disease risk that is clinically unactionable.
That said, some SNP tests can be medically important. Specific SNPs have been shown to affect drug metabolism, such as for warfarin or 5-FU. For some medications, evaluating the SNP profile affecting drug metabolism is becoming a part of routine care.
For more on the clinical use of GWAS, see the following review in Nature (2013).